1. Field of the Invention
The present invention relates to a semiconductor device, further detailedly relates to a semiconductor device which has small resistance, transmits a signal at high speed and is provided with a multilayer interconnection layer and its manufacturing process.
2. Description of the Related Art
To accelerate LSI, the miniaturization of a component and making wiring minute and a multilayer are promoted. For wiring, being minute, simultaneously the reduction of the resistance and the enhancement of the reliability are required. For the material of wiring, aluminum or an aluminum alloy (hereinafter called aluminum wiring) which is easy to work, is low-priced and has relatively small resistance has been widely used. However, it is required to more reduce the resistance of wiring and recently, wiring mainly made of a copper conductive layer (hereinafter called copper wiring) has been used for the material of wiring in LSI provided with minute wiring in place of aluminum wiring. For the resistivity in bulk of wiring material, aluminum is 3 to 3.5 μΩ·cm, copper is 2 μΩ·cm and the resistivity of copper is smaller. Copper wiring is excellent in resistance to stress migration and resistance to electromigration, compared with aluminum wiring and is also advantageous as the material of wiring in that respect.
Generally, for the production of aluminum wiring and copper wiring, in the case of aluminum wiring, after aluminum is deposited on a substrate, it is etched in a predetermined shape using photoresist by RIE (reactive ion etching) to remove unnecessary aluminum and wiring is formed, however, in the case of copper wiring, a damascening process that after a groove and a hole are formed on an insulating film, a copper film is deposited, unnecessary copper on the insulating film except the groove and the hole is removed and wiring is formed is used.
Generally, as a metallic thin film becomes thin, the resistivity increases differently from a case of bulk. In the case of a copper thin film, it is reported that when the copper thin film becomes extremely thin, the resistivity also increases. Further, it is reported in Fabrication and Performance Limits of sub 0.1 μm Cu interconnects, Materials Technology and Reliability for Advanced Interconnects and Low-k Dielectrics Symposium, Materials Research Society Symposium Proceedings, Vol. 612 by T. S. Kuan et al. on Apr. 23 to 27, 2000 that the increase of the resistance of copper wiring formed by the damascening process is further larger than the case of the thin film. For the reason, the scattering of electrons by irregularities of the surface of the wiring and the effect of a barrier film made of high-melting point metal around the copper wiring by the damascening process are reported (refer to Japanese published unexamined patent application No. 2000-216264). However, in case there are few irregularities on the surface of the wiring and the barrier film has little effect, the resistivity of the copper wiring also increases as the width w or the thickness t of the wiring becomes small.
As a result of examining the increase of the resistivity of copper wiring caused by making wiring minute in detail, it proves that the increase of the resistivity is caused by a fact that the mean free path of an electron of a copper atom is 45 nm and is large and the resistivity of the wiring is represented by a function also depending upon the width w of the wiring in addition to the thickness t (refer to Dependency upon thickness of Cu film of resistivity and grain structure, Proceedings of 7th research of atomic migration-stress problem in LSI wiring by Hanaoka et al. on Jul. 5 (Thursday) and 6 (Friday), 2000). In other words, it is considered that a phenomenon that when copper wiring is made minute, the resistance of the wiring abruptly increases is caused by the physical property of Cu itself and the phenomenon cannot be avoided by a method of manufacturing the wiring.
For such a reason, though copper wiring is used to reduce the resistance of wiring, the resistance of copper wiring made minute increases independent of its manufacturing process. Then, the realization of such wiring and the structure that the resistance of the wiring does not increase even if the wiring is made extremely minute has been desired.